I'm having the same problem that quicksilver is, albeit on a much newer computer. I have a retail version of PowerDVD Max 7 installed which plays DVDs just fine, as does windows media player, windows media center, creative mediasource, and the roxio player. But the Rifftrax player doesn't recognize that there is a DVD in the drive.
What I tried so far. I clicked on DVD Settings and selected use custom filters, and set both to the Cyberlink decoders, and I also tried the 10-odd other ones in the pull-down menus. nothing worked, still says no dvd in the drive when i click on load rifftrax
The only thing i can think of is that the rifftrax player supports only IDE DVD drives, and not SATA ones, or that it doesn't work with Vista. I'm at kind of a loss here, I've tried 2 DVDs so far. I'd rather not go the codec pack route, if at all possible, as every experience I've had with codec packs has resulted in problems so nightmarish and hard to fix that a complete re-install of windows was the only way to get everything working again, plus with the full version of PowerDVD installed, codecs shouldn't be the issue.
My specs:
Epox AF590 SLI2 (Nvidia 590 SLI chipset)
AMD Athlon64 X2 6000+
4GB Gskill DDR2 800
EVGA Geforce 8800GTX
Soundblaster X-fi
ASUS DRW-1814BLT SATA DVD Drive
Windows Vista Home Premium 32-bit
Any ideas?